System and method for on-demand near-patient humidification

ABSTRACT

A near-patient humidification system provides vapor to a respiratory breathing circuit. The system includes an expiratory gas conduit and an inspiratory gas conduit. A patient coupling member is provided for coupling the expiratory and inspiratory gas conduits to a patient interface. A vapor injection unit is located at least partially within the housing of the patient coupling member. The vapor injection unit heats a supply of fluid into vapor and injects the vapor into the inspiratory gas passage of the patient coupling member at a vapor injection location for providing moisture to the inspiratory gas flow. A method of simultaneously and independently controlling the temperature and humidity of inspiratory gas in a respiratory breathing circuit is performed by injecting vapor having a temperature determined as a function of measured temperatures and measured humidities of the breathing gas at different locations along the breathing circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional patent applicationNo. 62/413,154, filed Oct. 26, 2016, the disclosure of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to a system and method forproviding on-demand near-patient humidification to a respiratorybreathing circuit, and more particularly, to a system and method forproviding simultaneous independent control of temperature and humidityof a breathing gas.

BACKGROUND

Humidification during mechanical ventilation is often necessary toreduce drying of a patient's airways in order to prevent patientdiscomfort and possible complications, such as inspissation of airwaysecretions, hypothermia, and atelectasis. While passive humidifiers canprovide some relief, generally a heated humidifier is required tomaintain proper temperature and moisture of air delivered to a patient.

Conventional methods for humidifying gas often utilize a water chamber.The water chamber holds a quantity of water that is heated using aheating element. Dry gas is fed into the chamber and is humidified withthe heated water. The humidified gas then exits the chamber and isdelivered to a breathing circuit connected to the patient.Unfortunately, these conventional heating elements can often be bulkyand must be located away from patient. This arrangement can becumbersome and can also lead to the formation of condensation in thebreathing circuit.

For example, such conventional humidification systems supply heat andhumidity to respiratory gasses at an end of the breathing circuit near aventilator. Such an arrangement adds energy in the form of heat to waterwithin a reservoir, causing the water to evaporate and be transferred tothe patient via the respiratory airflow. However, predictive control ofhumidity to a predetermined target, goal, or setting is not permitted insuch conventional systems due to the variability of delivered humiditylevels in an inspiratory gas flow resulting from cooling andcondensation of vapor in the breathing circuit.

Most medical applications require airflow temperature to exceed ambienttemperature, resulting in conditions that permit vapor condensation onthe inner walls of the breathing circuit. However, conventionalhumidifiers allow the operator to grossly alter the humidity level byadjusting the reservoir temperature and the gas temperature within thebreathing circuit by using heated wires. International standard ISO 8185specifies that respiratory gasses should be humidified to a minimumabsolute humidity of 33 g/m³ at 37° C. While such conventionalhumidification systems may meet minimum requirements, they are notcapable of controlling the absolute humidity. Moreover, suchconventional humidification systems may be able to adjust, but notcontrol, the relative humidity (RH) between the minimum humidity andfully saturated air (i.e., at 100% RH).

Accordingly, there is a need for an improved humidification system andmethod that can provide on-demand near-patient humidification forrespiratory breathing circuits. Furthermore, there is a need for ahumidification system and method that permits simultaneous independentcontrol of the temperature and humidity of an inspiratory airflow of amedical respiratory ventilation circuit.

SUMMARY

The foregoing needs are met, to a great extent, by implementations ofthe system and method for on-demand near-patient humidificationaccording to the present disclosure. The present disclosure furtherprovides a method, process, or algorithm for controlling vaporadministered to a patient. Further, the system and method for on-demandnear-patient humidification according to the present disclosure intreatments utilizing high continuous flow, oscillating ventilators,non-invasive masks, or other myriad treatments. In accordance with oneimplementation, the near-patient humidification system for providingvapor to a respiratory breathing circuit comprises an expiratory gasconduit, an inspiratory gas conduit, a patient coupling member, a vaporinjection unit, and a vent coupling member. The expiratory gas conduitis configured to transport an expiratory gas flow from a patient. Theinspiratory gas conduit is configured to transport an inspiratory gasflow to a patient. The patient coupling member is configured to couplethe expiratory and inspiratory gas conduits to a patient interface. Thepatient coupling member has a housing defining an expiratory gas passagein communication with the expiratory gas conduit, an inspiratory gaspassage in communication with the inspiratory gas conduit, a proximalend having an expiratory gas outlet and at least one inspiratory gasinlet, and a distal end having an expiratory gas inlet and aninspiratory gas outlet. The vapor injection unit is located at leastpartially within the housing of the patient coupling member, andincludes a heater assembly configured to heat a supply of fluid intovapor and to inject the vapor into the inspiratory gas passage of thepatient coupling member at a vapor injection location for providinghumidity to the inspiratory gas flow.

According to one aspect of the disclosure, the vapor injection unitcomprises a vapor housing having a proximal end and a distal end, thevapor housing defining a housing lumen extending from the proximal endto the distal end. The vapor injection unit may further comprise acannula defining an inner lumen configured to receive a flow of water,and wherein the inner lumen is in fluid communication with theinspiratory gas passage of the patient coupling member.

According to another aspect of the disclosure, the heater assembly maybe an induction heater assembly or a conduction heater assembly. In theinduction heater assembly, and the vapor injection unit may comprise aninduction element surrounding at least a portion of the cannula. Theinduction element may comprise at least one helically wound metalliccoil. The induction element may comprise one or more electricalconductors configured to generate an oscillating magnetic dipole. Theinduction element may comprise at least two electrical conductorsconfigured to generate an oscillating magnetic multipole. Further, theat least two electrical conductors may be wires or a printed circuit.

According to another aspect of the disclosure, the near-patienthumidification system may comprise a heating element located inside thecannula and be at least partially surrounded by the induction element;wherein the induction element is configured to be excited by electricalcurrent supplied from a power assembly, to generate an oscillatingmagnetic field to create eddy currents in the heating element to heatthe heating element, and thereby heat the flow of water in the cannulaflowing past the heating element, to thereby vaporize the water intosteam which exits the vapor injection unit to be injected into theinspiratory gas passage. The heating element may comprise Mu-metal.Further, the heating element may include a magnetic material with arelative magnetic permeability greater than one. Further, the heatingelement may comprise a rolled foil spirally disposing a plurality oflayers of said foil. In another aspect, the heating element may comprisea wire mandrel and a foil wrapped around the wire mandrel in a spiralpattern disposing a plurality of layers of said foil.

According to another aspect of the disclosure, the housing includes aproximal end configured to releasably engage the expiratory andinspiratory gas conduits, and a distal end configured to releasablyengage a patient interface. The system may further comprise a ventcoupling member adapted to releasably couple the expiratory andinspiratory gas conduits to a ventilator. Further, the expiratory andinspiratory gas conduits may be concentrically arranged, such that theexpiratory gas conduit defines an inner conduit and the inspiratory gasconduit defines an outer conduit. The expiratory gas conduit may beconfigured to permit moisture to permeate through walls of theexpiratory gas conduit so that humidity or water vapor in the expiratorygas flow can be transferred to the inspiratory gas flow in theinspiratory gas conduit.

According to another aspect of the disclosure, the system may comprise afirst sensor configured to independently measure a temperature and/orhumidity of the inspiratory gas flow at a location upstream from thevapor injection location, and a second sensor configured toindependently measure a temperature and/or humidity of the of theinspiratory gas flow at a location downstream from the vapor injectionlocation. The first and second sensors may be spaced equally apart fromthe vapor injection location. The vapor injection unit may comprise avapor housing having a proximal end and a distal end, the vapor housingdefining a housing lumen extending from the proximal end to the distalend, and wherein the vapor injection unit includes a hub connected tothe proximal end of the vapor housing and being configured to connect toa fluid supply. A check valve may be provided proximal to the heatedelement.

According to another aspect of the disclosure, the vapor injection unitmay comprise a vapor housing having a proximal end and a distal end, thevapor housing defining a housing lumen extending from the proximal endto the distal end, and wherein the vapor housing comprises a thermallyinsulating material. The vapor injection unit may comprise a vaporhousing having a proximal end and a distal end, the vapor housingdefining a housing lumen extending from the proximal end to the distalend; wherein the vapor injection unit further comprises a cannuladefining an inner lumen configured to receive a flow of water; whereinthe inner lumen is in fluid communication with the inspiratory gaspassage of the patient coupling member; and wherein the cannula is madefrom a material selected from a metal, plastic, glass, ceramic, and acombination thereof.

According to another aspect of the disclosure, the vapor injection unitmay comprise a power assembly for connection to an electrical powersource. The power assembly may be located at the proximal end of thevapor housing.

The present disclosure also provides a method of simultaneously andindependently controlling the temperature and humidity of inspiratorygas in a respiratory breathing circuit comprises the steps of providinga near-patient humidification system; supplying a breathing gas to therespiratory breathing circuit; measuring a first temperature and a firsthumidity of the breathing gas at a location upstream from a vaporinjection unit; measuring a second temperature and a second humidity ofthe breathing gas at a location downstream from a vapor injection unit;and injecting vapor from the vapor injection unit into the respiratorybreathing circuit, the vapor having a vapor temperature determined as afunction of the measured first and second temperatures and the measuredfirst and second humidities of the breathing gas.

In another implementation of the present disclosure, a heating elementfor a humidification device to heat a fluid flowing through the devicecomprises a mandrel core, a rolled foil spirally wrapped around themandrel core to dispose a plurality of layers of said foil around themandrel core; and a plurality of gaps formed between adjacent layers ofwrapped foil and configured to provide a tortuous pathway for the fluidto travel in order to transfer heat from the foil to the fluid. In someaspects, the mandrel core may be a wire or a rod. Further, at least oneof the mandrel core and the rolled foil may comprise a magneticmaterial. The magnetic material may be selected from the groupconsisting of Mu-metal, Alumel, nickel, iron, and permalloy. The rolledfoil spirally wrapped around the mandrel core may comprise a jelly rollshape. The rolled foil may further comprise at least three or fouradjacent layers. The rolled foil spirally wrapped around the mandrelcore may further comprise a spiral cross-section.

Certain aspects of the system and method for on-demand near-patienthumidification have been outlined such that the detailed descriptionherein may be better understood. It is to be understood that thehumidification system and method are not limited in application to thedetails of construction and to the arrangements of the components setforth in the following description or illustrated in the drawings. Thehumidification system and method is capable of aspects in addition tothose described, and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as in the Abstract, are for the purpose ofdescription and should not be regarded as limiting.

As such, the conception upon which this disclosure is based may readilybe utilized as a basis for the designing of other structures, methods,and systems for carrying out the several purposes of the humidificationsystem and method. It is understood, therefore, that the claims shouldbe regarded as including such equivalent constructions insofar as theydo not depart from the spirit and scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the disclosure may be readily understood, aspects of thehumidification system and method are illustrated by way of examples inthe accompanying drawings.

FIG. 1 is a perspective view of an induction heater assembly of ahumidification system according to a first implementation of thedisclosure.

FIG. 2 is a cross-sectional view of the induction heater assembly of thehumidification device of FIG. 1.

FIG. 3 is a front view of the induction heater assembly of thehumidification device of FIG. 1.

FIG. 4 is a cross-sectional view of a heating element assembly of thehumidification device according to an aspect of the disclosure.

FIG. 5 is cross-sectional view of another implementation of a heatingelement assembly of a humidification device.

FIG. 6 is schematic system diagram of a humidification device of thedisclosure coupled to a respiratory breathing circuit.

FIG. 7 is a schematic diagram of a multi-limb humidification systemaccording to another implementation of the disclosure.

FIG. 8 is a schematic view illustrating an apparatus that may beincorporated into or as part of a breathing gas circuit in accordancewith one or more implementations of the present disclosure.

FIG. 9 is a schematic cross-sectional view taken along line 9-9 of FIG.8.

FIG. 10 is a schematic cross-sectional view illustrating the apparatusof FIG. 8 according to another implementation of the disclosure.

FIG. 11 is an exploded perspective view of a single-limb humidificationsystem according to another implementation of the disclosure.

FIG. 12 is a side elevation cross-sectional view of the humidificationsystem of FIG. 11.

FIG. 13 is a front cross-sectional view of the system taken along line13-13 of FIG. 12.

FIG. 14 is a side elevation cross-sectional view of a patient couplingmember according the present disclosure.

FIG. 15 is a front cross-sectional view of the system taken along line15-15 of FIG. 14.

FIG. 16 is a perspective side cross-sectional view of a vapor injectionunit according to the present disclosure.

FIG. 17 is a front cross-sectional view of a heating element accordingto the present disclosure.

FIG. 18 is a side elevation view of a vent coupling member according tothe present disclosure.

FIG. 19 is a top cross-sectional view of the vent coupling member takenalong line 19-19 of FIG. 18.

FIG. 20 is a front cross-sectional view of the vent coupling membertaken along line 20-20 of FIG. 18.

FIG. 21 is a schematic diagram of the humidification system according toan implementation of the disclosure.

FIG. 22 is a schematic diagram of a single-limb humidification systemaccording to another implementation of the disclosure.

FIG. 23 is a flowchart depicting a algorithm for determining patientbreathing cycle according to an aspect of the disclosure.

Implementations of the humidification system and method are describedwith reference to the drawings, in which like reference numerals referto like parts throughout.

DETAILED DESCRIPTION

The present disclosure is directed to a respiratory humidificationsystem and method for on-demand near-patient humidification. Therespiratory humidification system may comprise a humidification deviceconfigured to add moisture to a breathing gas in order to a control ahumidity level thereof. As used herein, a “breathing circuit” or“breathing gas circuit” may be any arrangement of tubes or conduitswhich carries gases to be administered to and from a patient, such asfrom a ventilator, and which may include additional accessories ordevices attached thereto. Such “breathing gases” may include oxygen, airor any component thereof, and are configured to absorb high levels ofmoisture and/or be humidified prior to administration to a patient, orduring administration to a patient, and be suitable for medicalapplications.

One implementation of the humidification device may include a heaterassembly 100 and a heating element assembly 200. The heater assembly 100may be an induction heater assembly in some implementations, oralternatively, a conduction heater assembly in other implementations.For instance, such an heater assembly 100 that forms part of thehumidification device is illustrated in FIG. 1. The heater assembly 100may include a housing 102 having a proximal end 104 and a distal end106. The heater assembly 100 may also include a power and controlsinterface assembly 108 connected to the housing 102. A plurality ofcooling fins 110 may extend from a portion of the housing 102 and thepower and controls interface assembly 108. In some aspects, the coolingfins 110 may extend from a portion of the housing 102 and the power andcontrols interface assembly 108.

FIG. 2 illustrates a cross-sectional view of the heater assembly 100 ofFIG. 1. The housing 102 may define a housing lumen 112. The housinglumen 112 may extend from the proximal end 104 to the distal end 106.The housing lumen 112 may be configured to receive a heating elementassembly 200 (shown in FIG. 4) at the proximal end 104. The shape of thehousing lumen 112 may match the shape of the heating element assembly200. For example, the diameter of the housing lumen 112 may be greatertowards the proximal end 104 than the diameter of the housing lumen 112at the distal end. According to another aspect of the disclosure, theheating element assembly 200 may be disposable.

The heater assembly 100 may include an induction element 114 locatedalong the housing lumen 112. The induction element 114 may be located ata distal region 116 opposite from a proximal region 118 of the housinglumen 112. In other aspects, the induction element 114 may span from thedistal region 116 to the proximal region 118 of the housing lumen 112.In some aspects, the induction element 114 may be an induction coilformed from a single or multiple enameled wires. If the inductionelement 114 is formed from multiple wires, the multiple wires may betwisted to form a Litz wire. A Litz wire configuration can reduce powerloss and heat generated by the “skin effect” at high alternating current(AC) frequencies. The induction element 114 may be center-tapped, and apositive voltage may be supplied at the center tap. The ends of theinduction element 114 may be alternately switched to ground to generatean oscillating magnetic field within the interior of the inductionelement 114. The oscillating magnetic field created from the inductionelement 114 may produce eddy currents to heat objects placed within thehousing lumen 112. It should further be appreciated that the inductionelement may comprise a rectangular cross-section magnet wire whichprovides similar results as the aforementioned Litz wire. Further,according to another aspect, power to the induction element 114 may beswitched to ground, or between positive and negative voltages. Thevoltage waveform may be square for providing most efficiency, sinusoidalfor minimizing EMI, or another waveform such as triangular or sawtooth.

In other aspects, the induction element 114 may be a pair of parallelelectrical conductors configured to generate a dipole. The pair ofparallel electrical conductors may extend within the housing lumen 112parallel to a center axis 120. The pair of parallel electricalconductors may be insulated wires or conductive tracks formed onto aflexible printed circuit. The printed circuit may be formed to fit intothe housing lumen 112 of the heater assembly 100. For example, in theaspect shown in FIG. 2, the induction element 114 as a printed circuitmay be shaped like a hollow cylinder. To generate a dipole, a positivevoltage may be supplied to one of the electrical conductors. The twoends of the other electrical conductor may be alternately switched toground at a high frequency in order to generate an oscillating magneticfield within the housing lumen 112.

In further aspects, the induction element 114 may be more than two pairsof electrical conductors configured to generate an oscillating magneticfield having multiple poles, such as a quadrupole, hexapole, octupole,or another multipole system with either an even or odd number ofmagnetic poles. The pairs of electrical conductors may similarly extendwithin the housing lumen along the center axis 120. The electricalconductors may be insulated wires or conductive tracks formed onto aflexible printed circuit board. A positive voltage may be supplied toone set of electrical conductors. The set of electrical conductors maybe alternately switched to ground at a high frequency to create arapidly oscillating magnetic field. In other aspects, a circuit may beused to switch the polarity of each end of the induction element 114 toimprove the efficiency of the induction element 114.

In the various aspects described above, the induction element 114 maygenerate an oscillating magnetic field with frequencies between up to200 kHz. In further aspects, electromagnetic shielding, specificallyradio frequency shielding, may be necessary such that the heaterassembly 100 meets various regulatory electro-magnetic emissionrequirements.

As mentioned previously, a plurality of cooling fins 110 may extend froma portion of the housing 102. In other aspects, the cooling fins 110 mayalso extend from an exterior surface of the power and controls interfaceassembly 108. The cooling fins 110 may increase the rate of heattransfer from the heater assembly 100 by increasing the amount ofsurface area of the heater assembly 100 exposed to the air. In someaspects, the cooling fins 110 may be used to transfer heat from theinduction element 114 into the gas flow stream by extending into the gasflow line. In some aspects, the cooling fins 110 may be made from thesame material as the housing 102. In other aspects, the cooling fins maybe made from material with a greater heat transfer coefficient than thatof the material for the housing 102 in order to improve the coolingabilities of the cooling fins 110. The plurality of cooling fins 110 mayhave a circular, square, elliptical, rectangular, or other similarshape. The shape and size of the cooling fins 110 may be the same or mayvary among the plurality of cooling fins 110. For instance, the coolingfins may be any shape intended to reduce external surface temperaturesthat may contact the patient or user.

The heater assembly 100 may also include a thermal insulator 122. Thethermal insulator 122 may be located between the induction element 114and the inner surface 124 of the housing 102. The thermal insulator 122may extend radially from the outer surface 126 of the induction element114. The thermal insulator 122 may be made from a material with lowthermal conductivity to reduce heat transfer away from the inductionelement 114, which may increase the transfer of heat generating by theinduction element 114 through the housing lumen 112 and cannula 202 intothe fluid. Materials for the thermal insulator 122 may include ceramics,glass, composite materials such as glass-bonded mica (Mykroy/Mycalex),fiberglass, insulating plastics, or other suitable materials. Thethermal insulator 122 may be formed from extruded tubing or anotherprocess suitable to shape the thermal insulator 122 to fit within thehousing 102. Alternatively, a thermally conductive material may beselected for the thermal insulator 122 to transfer heat from theinduction element 114 towards the cooling fins 110 and/or into therespiratory gas.

The heater assembly 100 may include thermocouple electrical contacts 128formed on an inner surface 124 of the housing 102. The thermocoupleelectrical contacts 128 may be configured to engage correspondingthermocouple conductors (shown in FIG. 4) on the heating elementassembly 200. The thermocouple electrical contacts 128 may be formed atthe proximal region 118 of the housing 102. The thermocouple electricalcontacts 128 may be in electrical connection with the power and controlsinterface assembly 108. Once the heating element assembly 200 isreceived within the heater assembly 100 and the thermocouple electricalcontacts 128 engage the corresponding exposed thermocouple conductorsurfaces 218 and 220, an electrical circuit will be completed within theheater assembly 100. In other aspects, the heater assembly 100 may useother devices, such as thermistors or resistance temperature detectors(RTDs), to measure temperature.

The heater assembly 100 may also include a non-magnetic tube 130 withinand at the proximal region of the housing lumen 112. The non-magnetictube 130 may only extend a portion of the length of the housing lumen112. The non-magnetic tube 130 may be configured to receive the heatingelement assembly 200. The non-magnetic tube 130 may prevent directcontact between the induction element 114 and the heating elementassembly 200 once the heating element assembly 200 is received withinthe heater assembly 100. The spacing between the induction element 114and the heating element assembly 200 may improve performance of theinduction element 114. The non-magnetic tube 130 may be made fromplastic, glass such as borosilicate glass, ceramics, heat-resistantplastics, or other suitable non-magnetic materials.

As shown in FIG. 2, the power and controls interface assembly 108 isconnected to the housing 102. The power and controls interface assembly108 and housing 102 may be a single component. The power and controlsinterface assembly 108 may be implemented as a connector receptacle orother interface to facilitate a quick connection and/or disconnectionwith an electrical power source and/or control interface. In otheraspects, the power and controls interface assembly 108 may include anelectrical power source and be removably coupled to the housing 102. Thepower and controls interface assembly 108 may provide electrical powerto the induction element 114 and/or thermocouple electrical contacts128. The electrical connection may be established using insulated wiresand/or flexible printed circuits. The power and controls interfaceassembly 108 may be oriented along a power assembly axis 132. In theaspect shown in FIG. 2, the power assembly axis 132 may be at an acuteangle to the center axis 120 of the housing 102. In other aspects, thepower assembly axis 132 may be at any angle perpendicular or parallel tothe center axis 120.

FIG. 3 illustrates a front view of a heater assembly 100. The power andcontrols interface assembly 108 may have a plurality of electricalcontacts 134 to engage an electrical power source (not shown). Theelectrical contacts 134 may provide electrical power to the thermocouplecontacts 128. The power and controls interface assembly 108 may alsoinclude a plurality of electrical pins 136. The electrical pins 136 maybe used to facilitate an electrical connection with an electrical powersource and/or control interface.

FIG. 4 illustrates a heating element assembly 200 that forms anotherpart of the humidification device according to one implementation foruse in the humidification system of the present disclosure. The heatingelement assembly 200 includes a cannula 202 connected to a hub 204. Thecannula may be a tube configured to be removably received within thenon-magnetic tube 130 and/or housing lumen 112 of the heater assembly100. The cannula 202 may be made from materials such as stainless steel,glass, ceramic, or other suitable materials. The cannula 202 may bemagnetic or non-magnetic. The cannula 202 may extend between a proximalend 206 and a distal end 208. The proximal end 206 may be connected tothe hub 204 while the distal end 208 may be configured to be insertedinto the housing lumen 112 of the heater assembly 100. The hub 204 maybe formed around a portion of cannula 202 in an overlapping region 210.The hub 204 may have a standardized Luer connection or a customconnection.

The heating element assembly 200 may include a heating element 212located within the cannula 202. The heating element 212 may be made froma magnetic material such as Mu-metal, Alumel, nickel, iron, permalloy,or other materials with a high relative magnetic permeability. Theheating element 212 may be a tube, a solid cylinder such as a rod orwire, a matrix of cylinders, a sintered cylinder, a porous cylinder, asheet, a spiral sheet, a coil, or any combination of the foregoing. Itshould also be appreciated that the heating element 212 may comprise arolled foil having a jelly roll shape, as will be described in greaterdetail below. As illustrated in FIG. 4, the heating element 212 may be atwisted or helical coil of multiple wires. The heating element 212 maybe located at a distal region 214 of the cannula. In other aspects, theheating element 212 may extend from the proximal end 206 to the distalend 208.

The heating element 212 may be configured to overlap with the inductionelement 114 when the heating element assembly 200 is removably receivedwithin the heater assembly 100. The heating element 212 may beconfigured to interact with the oscillating magnetic field generated bythe induction element 114. The heating element 212 can have a highmagnetic permeability because the efficiency of induction heating withinthe heating element 212 may be greater. The heating element 212 can havea greater surface area to increase the efficiency of heat transferbetween the fluid pumped into the cannula and the heating element 212.

The heating element assembly 200 may include thermocouples conductors216. The thermocouple conductors 216 may allow a user to monitor and/orprovide closed-loop temperature control of the heating element 212. Thethermocouple conductors 216 may be integrated with the heating element212 as a single component. In other aspects, the thermocouple conductors216 may be a separate component from the heating element 212. Asillustrated in FIG. 4, the thermocouple conductors 216 are separatecomponents form the heating element 212 with the heating element 212located at the distal region 214 of the thermocouple conductors 216. Inother aspects, one of the thermocouple conductors 216 may be integratedinto the cannula 202 and/or be placed in contact with the fluid path,which may allow the cannula 202 and/or a fluid to act as a conductor,such that at least a portion of the measured thermocouple voltage ismeasured across the cannula 202 and/or fluid.

One or both of the thermocouple conductors 216 may be made from amagnetic material, such as Mu-metal, Alumel, nickel, iron, permalloy, oranother alloy, to allow the thermocouple conductors 216 to interact withthe oscillating magnetic field generated by the induction element 114and produce heat, which increases the efficiency of the heating element212. The thermocouple conductors 216 may be made from the same materialas the heating element 212 to simplify fabrication of the heatingelement assembly 200. In other aspects, at least one of the thermocoupleconductors 216 may be made from a non-magnetic alloy to reducegeneration of induction heating within the non-magnetic leg and improveaccuracy of the temperature measurements. Non-magnetic materials mayinclude copper, Nicrosil, Nisil, Chromel, Constantan, or other similaralloys. A material with low thermal conductivity for the non-magneticleg can further improve accuracy.

The thermocouple conductors 216 may correspond to a positive electrodeand a negative electrode. The voltage differential between thethermocouple conductors 216 may vary depending on the temperature, whichmay be used to determine and control the temperature of the heatingelement assembly 200. The thermocouple conductors 216 may have exposedthermocouple conductor surfaces 218 and 220. The exposed thermocoupleconductor surfaces 218 and 220 may be located on a surface the hub 204.The exposed thermocouple conductor surfaces 218 and 220 may beconfigured to engage the thermocouple electrical contacts 128 on theheater assembly 100 once the heating element assembly 200 is receivedwithin the housing 102 to allow the voltage to be read.

For operation of the humidification device, the heating element assembly200 may be inserted into the housing 102 of the heater assembly 100. Theinduction element 114 may be excited to generate an oscillating magneticfield, which may create eddy currents within the heating element 212.The eddy currents generated in the heating element 212 may heat theheating element 212. Water may be pumped into the heater assembly 100 atthe proximal end 104 and through the cannula 202 of the heating elementassembly. As water travels past the heating element 212, the water mayrapidly absorb heat and vaporize into steam. As steam forms, the rapidexpansion may cause pressurized steam to be injected into a patient'sbreathing circuit gas conduit and humidify the gases. The steam pressuremay also apply force against the supply water. The process may repeat ina cyclical fashion resulting in steam periodically injected into thepatient's breathing circuit.

Although the humidification device may include the heater assembly 100and the heating element assembly 200 as separate units as shown in FIGS.2 and 4, in other aspects, the heater assembly 100 and the heatingelement assembly 200 may be combined to form a single integral unit. Forexample, the heating element 212 and thermocouple conductors 216 may beintegrated into the heater assembly 100 to form the humidificationdevice. The combined heater assembly 100 and heating element assembly200 may be designed to be disposable and/or replaceable after a limitednumber of uses. Further, in other implementations of the disclosure, theheating element 212 may be a conduction heating element configured to beheated by conduction.

FIG. 5 illustrates another implementation of the heating elementassembly 300 that forms part of a humidification device according toanother aspect of the disclosure. The heating element assembly 300 issimilarly configured to be removably received within the housing 102 ofthe heater assembly 100. The heating element assembly may include acannula 302, hub 304, and heating element 312 similar to the aspectsdescribed above with respect to FIG. 4. In addition, the heating elementassembly 300 may include a check valve 314. The check valve 314 may be avalve that only permits fluid to flow from the proximal end 316 to thedistal end 318. The check valve 314 may be implemented with at least oneof a ball check valve, a diaphragm check valve, a swing check valve, astop-check valve, a pneumatic non-return valve, or another similarmechanical valve. The check valve 314 may close the supply of waterentering the heating element assembly 300 as a result of steam pressureformed within the heating element assembly 300.

FIG. 6 is a schematic diagram illustrating a standard respiratory system400A that includes a ventilator 401 and a patient or patient interface402, which are fluidly interconnected by a respiratory breathing circuit403, as is known in the art. In the standard respiratory system 400A, anembodiment of the humidification device having the heater assembly 100may be coupled to the respiratory breathing circuit 403 so that steammay be injected into a patient's breathing circuit gas conduit at somepoint along the respiratory breathing circuit 403, to thereby humidifythe gases flowing therein, and deliver the humidified gas to the patientor patient interface 402.

FIG. 7 is a schematic diagram illustrating an implementation of amulti-limb respiratory humidification system 400B for on-demandnear-patient humidification according the present disclosure, whereinthe respiratory breathing circuit comprises at least one expiratory limb404 defining an expiratory gas conduit configured to transportexpiratory gas from the patient 402 to the ventilator 401, and at leastone inspiratory limb 405 defining an inspiratory gas conduit configuredto transport inspiratory gas from the ventilator 401 to the patient 402.The at least one expiratory limb 404 and the at least one inspiratorylimb 405 of the multi-limb system may be separate and spaced apart fromeach other. In one aspect, the expiratory and inspiratory conduits maybe non-concentric. Further, in the multi-limb respiratory humidificationsystem 400B, an embodiment of the humidification device of the presentdisclosure having the heater assembly 100 may be coupled to theinspiratory limb 405 at a location proximate the patient 402 so thatsteam may be injected into a dry breathing gas at a location near thepatient to thereby humidify the breathing gas, and efficiently deliverthe humidified gas to the patient.

In another implementation of a multi-limb respiratory humidificationsystem for on-demand near-patient humidification according the presentdisclosure, the at least one expiratory limb 404 and/or the at least oneinspiratory limb 405 of the respiratory breathing circuit may comprise amoisture removal and condensation and humidity management apparatus asdescribed in U.S. Patent Publication No. 2016/0303342, which is herebyincorporated herein by reference, in order to remove or decrease watervapor, moisture, or condensate from the respective gas conduit.

It should be appreciated that the at least one expiratory or inspiratorylimb 404, 405 of the respiratory breathing circuit may comprise otherembodiments of the moisture removal and condensation and humiditymanagement apparatus. For example, FIG. 8 is schematic view showing oneembodiment of a moisture removal and condensation and humiditymanagement apparatus 410 configured to rapidly remove water vapor orcondensate from a humidified medical gas traveling therethrough. Themoisture removal and condensation and humidity management apparatus 410for a breathing circuit may include a section or length of breathingcircuit tubing 411 defining a breathing gas conduit 412 for a flow (B)of breathing gas therein. The breathing gas flows from a first, upstreamend 410A of the apparatus 410 proximate to a patient, through thebreathing gas conduit 412 defined within the apparatus 410, and to asecond, downstream end 410B of the apparatus 410 distal of the patient.The breathing gas may have a first humidity level and a level ofmoisture therein, which may be calibrated by the user based on the needsof the patient. In some embodiments, the length of breathing circuittubing 411 is in an expiratory limb of a breathing circuit, for example,positioned somewhere between a patient and a ventilator.

The apparatus 410 may also include a dry gas conduit 414 adjacent to atleast a portion of the breathing gas conduit 412 between the upstreamend 410A and downstream end 410B, for a dry gas flow (D) therein. Thedry gas flow (D) is configured to have a second humidity level which islower than the first humidity level within the breathing gas conduit(B). In some embodiments, the dry gas conduit 414 may extend the entirelength of the breathing gas conduit 412 to optimize moisture transfer.However, in some embodiments, the dry gas conduit 414 may extend lessthan the entire length of the breathing gas conduit 412. The dry gasconduit 414 may include a closed end 416 on the upstream end 410A, anddownstream end 410B an outlet 418 at the downstream end 410B. The outlet418 may be in communication with a source of suction and/or the ambientenvironment around the apparatus 410. In some embodiments, the outlet418 may be in communication with a filter 420.

The apparatus 410 may further include a feeding conduit 424 configuredto supply dry gas to the dry gas conduit 414. As depicted in FIG. 8, thefeeding conduit 424 may include an inlet 426 at the downstream end 410Bof the apparatus 410, and an outlet 428 at the first end 410B of theapparatus 410, such that the feeding conduit 424 extends through atleast a portion of the dry gas conduit 414. For example, the feedingconduit 424 may extend greater than half of the length of the dry gasconduit 414. In some embodiments, the feeding conduit 424 may extendsubstantially the entire length of the dry gas conduit 414.Advantageously, the feeding conduit 424 may allow the inlet 426 andoutlet 418 for dry gas of the apparatus 410 to be further away from thepatient, reducing any potential safety risk to the patient. Thisprevents any potential sparking caused by the ingress and egress of thedry gas proximate the patient. Furthermore, by providing the outlet 418of the feeding conduit 424 at the upstream end 410A within the dry gasconduit 414, the apparatus 410 may provide a large surface area formoisture/humidity transfer from the breathing gas conduit 412 to the drygas conduit 414. In some embodiments, a flow or volume control element430 (e.g., a valve) may be connected to the inlet 426 of the feedingconduit 424 and configured to control the flow of dry gas into thefeeding conduit 424.

FIG. 9 is a schematic cross-sectional view illustrating the apparatus410 of FIG. 8 of one or more embodiments of the present disclosure. Asshown in the embodiment of FIGS. 8-9, the dry gas conduit 414 may be anannular flow space which is concentric with breathing gas conduit 412.For example, the breathing circuit tubing 411 may include an inner tube432 defining the breathing gas conduit 412, and an outer sleeve or tube434 surrounding the inner tube 432 and defining the dry gas conduit 414.The dry gas conduit 414 thereby may include an annular conduit 436defined between the inner tube 432 and outer tube 434. Alternatively, insome embodiments, the inner tube 432 may define the dry gas conduit 414and the annular conduit 436 between the inner tube 432 and the outertube 434 may include the breathing gas conduit 412. As depicted, thefeeding conduit 424 may extend through the dry gas conduit 414. One orboth, of the inner tube 432 and the outer tube 434 may includecorrugated tubing. In the present disclosure, a moisture transmissionpathway may be positioned between the breathing gas conduit 412 and thedry gas conduit 414. For example, a sufficient stretch of surface areaof the breathing circuit tubing 411 may be shared between the breathinggas conduit 412 and the dry gas conduit 414 enabling transfer ofmoisture between the flow of breathing gas (B) and the flow of dry gas(D), as further described below.

The present disclosure provides one or more embodiments which providethe moisture transmission pathway between the breathing gas conduit 412and the dry gas conduit 414, lowering the moisture and/or humidity inthe flow of breathing gas (B) by transferring the moisture and/orhumidity to the dry gas flow (D). For example, in FIG. 9, the moisturetransmission pathway (T) may occur between the higher humidity breathinggases in breathing gas conduit 412 and the lower humidity dry gas flowin dry gas conduit 414. A user may increase or decrease the level of drygas supplied to the dry gas conduit 414 to manage or remove thecondensate which may be transferred from the breathing gas (B) to thedry gas (D). The moisture level thus may be reduced from within thebreathing gas flow (B) and transferred to the dry gas flow (D).

In some embodiments, such as shown in FIG. 9, the breathing circuittubing 411 may include a permeable portion or membrane (as depicted inbroken lines) along part or all of the inner tube 432. The permeableportion may be permeable to water vapor but impermeable to liquid water,such that the moisture transmission pathway (T) is provided by thepermeable portion of the breathing circuit tubing 411. The permeableportion may include one or more materials that are water vaporbreathable and allow passage of water vapor, as is well known to thoseof ordinary skill in the art. The permeable portion may form some or allof the walls of the breathing gas conduit 412 (e.g., inner tube 432) andmay include a single, or composite layer of water vapor breathablemedium. For example, in some embodiments, the permeable portion mayinclude an inner layer and an outer layer having differentpermeability/wicking properties. A first wicking layer may be providedas an inner layer of inner tube 432 and may be configured to contact thebreathing gas flow (B) inside of the inner tube 432. The wicking layermay be made of one or more wicking materials that allow for adsorptionand/or absorption of moisture and/or water in any phase (e.g., gasand/or liquid), for example, through capillary action. The permeableportion may also include an outer layer of water vapor breathablematerial that permits the passage of water vapor only, while notpermitting passage of liquid water.

Examples of wicking material of the permeable portion include knittedand/or non-woven cloth or fabric. The wicking material may be naturaland/or synthetic, such as polyester, polyester and polypropylene blends,nylon, polyethylene or paper. The wicking material may also includemicrofilaments and/or microfiber material such as Evolon® brand fabricmaterial made by Freudenberg & Co. KG. One particular example of wickingmaterial may be a non-woven material of 70% polypropylene and 30%polyester. Another example of the wicking material may be Evolon® brandfabric material having a weight of 60 or 80 grams per square meter.Examples of the outer layer of water vapor breathable material includeSympatex® brand water vapor permeable membranes made of polymers made bySympatex Technologies, including monolithic hydrophilic polyester estermembrane, including, as one example, a 12 micron thick membrane. Theouter tube 434 may include a more rigid material than the inner tube432, to prevent the inner tube 432 from being damaged and/or punctured.

In some embodiments, the breathing circuit tubing 411 may, additionallyor alternatively, include one or more small openings or perforations(not shown) in the inner tube 432 which permit drainage of liquid waterfrom the breathing gas conduit 412 to the dry gas conduit 414.Therefore, a second moisture transmission pathway T1 may be provided bythe one or more perforations between the breathing gas flow (B) and drygas flow (D), as shown in FIG. 9. Although, the transmission pathway (T)and the second transmission pathway (T1) are depicted in the samecross-sectional view of FIG. 9, the transmission pathways (T, T1) may beprovided in the alternative and/or at different portions along thebreathing circuit tubing 11. The transmission pathway (T) and the secondtransmission pathway (T1) may be provided in a gradient along the lengthof the inner tube 432. For example, in some embodiments, the inner tube432 may have more permeability at the upstream end 410A than thedownstream end 410B, increasing moisture transfer when the breathing gasenters the breathing gas conduit 412 reducing condensation in remaininglength of the inner tube 432. In some embodiments, the inner tube 432may have more permeability on the downstream end 410B than the upstreamend 410A, increasing moisture transfer when the moisture of thebreathing gas is lower.

FIG. 10 is a schematic cross-sectional view illustrating the apparatusof FIG. 8 of one or more additional embodiments of the presentdisclosure. As depicted in FIG. 10, a breathing circuit tubing 451 mayinclude a tube 472 including a breathing gas conduit 462 configured toreceive a flow of breathing gas flow (B). The breathing gas may have afirst humidity level and a first level of moisture. The tube 462 mayalso include a dry gas conduit 464 configured to receive a dry gas flow(D). The dry gas flow may have a second humidity level lower than thefirst humidity level, and/or a second level of moisture lower than thefirst level of moisture. The dry gas conduit 464 may be adjacent to atleast a portion of the breathing gas conduit 462. A feeding conduit 474may extend through the dry gas conduit 464. As further depicted in FIG.10, a moisture transmission pathway (T2) may be provided between thebreathing gas conduit 462 and the dry gas conduit 464, such thatmoisture and/or humidity may be transferred from the breathing gas (B)to the dry gas flow (D) based on the differential humidity/moisturelevels. In the embodiment of FIG. 10, the breathing gas conduit 462 anddry gas conduit 464 may share a common dividing wall 480 providing themoisture transmission pathway (T2). For example, the moisturetransmission pathway (T2) may be provided by a permeable portion ormembrane (depicted as broken lines) incorporated into part or all of thedividing wall 480, as described herein, or a series of perforations inpart or all of the dividing wall 480, as also described herein. Thepermeable portion may be permeable to water vapor but impermeable toliquid water and may include one or more layers, including a wickinglayer, as described above.

In one or more embodiments of the present disclosure, the dry gasconduit 414, 464 may be closed to ambient air around the apparatus 410.The dry gas conduit 414, 464 therefore can be configured to provide astream of dry gas flow at humidity levels which are significantly lowerthan the humidity in the breathing gas conduit 412, 462. In someembodiments, the apparatus 410 may include one or more sensorsconfigured to detect the first humidity level of the breathing gasconduit 412 and the second humidity level of the dry gas conduit 414.The present disclosure therefore uses the differential between humidityor moisture content between the respective flows in the breathing gasconduit 412, 462, compared to the dry gas conduit 414, 464, which allowsfor greater extraction or diffusion of moisture and humidity from thebreathing gas flow to the dry gas flow, which is further assisted by theconvective action of the dry gas flow along the common surface areashared between the breathing gas conduit 412, 462, and the dry gasconduit 414, 464, such as along inner tube 432, or common dividing wall480.

Referring to FIGS. 11 and 12, an implementation of a single-limbrespiratory humidification system 500 for on-demand near-patienthumidification according to the present disclosure is shown. Thesingle-limb respiratory humidification system 500 may comprise ahumidification device according to another embodiment of the disclosurethat is configured to add moisture to a breathing gas in order to adjusta humidity level thereof. The humidification device may include apatient coupling member 510, a vapor injection unit 540, an expiratorygas conduit 582, and an inspiratory gas conduit 584. The humidificationsystem may also comprise a vent coupling member 590. The patientcoupling member 510 is configured to couple the expiratory andinspiratory gas conduits 582, 584 to a patient or patient interface,such as an endotracheal tube, a breathing mask, or a nasal cannula,among others. In one aspect of the disclosure, the patient couplingmember 510 may be provided at a location near the patient in order toavoid condensation buildup within the inspiratory gas conduit 584. Thevent coupling member 590 is configured to couple the expiratory andinspiratory gas conduits 582, 584 to a ventilator and/or a flow meter toassist with supplying and/or circulating an airflow to the patient.

As illustrated in FIG. 13, the expiratory gas conduit 582 may beprovided within the interior of the inspiratory gas conduit 584 to forma single limb breathing circuit in order to assist with humidificationof the inspiratory gas flow, as will later be discussed in greaterdetail. In such a single limb arrangement, the expiratory gas conduit582 defines an inner conduit and the inspiratory gas conduit 584 definesan outer conduit. Further, the expiratory and inspiratory gas conduits582, 584 may be coaxially aligned so that expiratory gas is permitted toflow within the interior space of the expiratory gas conduit 582, andinspiratory gas is permitted to flow within the space 585 formed betweenthe inspiratory gas conduit 584 and the expiratory gas conduit 582. Moreparticularly, the expiratory and inspiratory gas conduits 582, 584 ofthe single limb implementation shown in FIGS. 11-13 may comprisecylindrically shaped flexible tubing that are concentrically arranged.Alternatively, it should be appreciated that the expiratory gas conduit582 and the inspiratory gas conduit 584 may be non-concentricallyaligned.

Referring to FIG. 14, the patient coupling member 510 comprises ahousing 512 defining an expiratory gas passage 514 in communication withthe expiratory gas conduit 582, and an inspiratory gas passage 516 incommunication with the inspiratory gas conduit 584. In particular, aproximal end 517 of the housing 512 may include an expiratory gas outlet522 and at least one inspiratory gas inlet 524, and a distal end 518 ofthe housing 512 may include an expiratory gas inlet 526 and aninspiratory gas outlet 528. In one aspect of the disclosure, forexample, three inspiratory gas inlets 524 may be provided to allow gasfrom the inspiratory gas conduit 584 to enter into the inspiratory gaspassage 516 of the housing 512. Further, the proximal end 517 of thehousing 512 may include an expiratory fitting portion 532 adapted tosealingly connect to an end of the expiratory gas conduit 582, and aninspiratory fitting portion 534 adapted to sealingly connect to an endof the inspiratory gas conduit 584. For example, the expiratory andinspiratory gas conduits 582, 584 may mate with the respectiveexpiratory and inspiratory fitting portions 532, 534 of the patientcoupling member 510 in a sealing manner, such as with a press-fitconnection or a bonded connection using adhesive, in order to preventleakage. The expiratory and inspiratory gas passages 514, 516 of thepatient coupling member 510 may be separated by a barrier wall 520 sothat expiratory gas and inspiratory gas do not mix within the housing512.

According to another aspect of the disclosure, a vapor injection unit540 may be disposed within the patient coupling member 510. The vaporinjection unit 540 is configured to inject vapor into the inspiratorygas passage 516 of the patient coupling member 510, as will be discussedin greater detail below. The patient coupling member 510 may comprise acap or cover 530. In one implementation, the vapor injection unit 540may be disposed entirely within the housing 512. In anotherimplementation, the vapor injection unit 540 may be at least partiallydisposed within the housing 512.

In the implementation shown in FIGS. 14 and 15, the cap or cover 530 islocated directly adjacent to the expiratory air passage 514, and thevapor injection unit 540 is disposed within both the expiratory andinspiratory gas passages 514, 516. An access hole 521 provided in thebarrier wall 520 of the patient coupling member 510 permits the vaporinjection unit 540 to pass through the barrier wall 520 such that adispensing end of the vapor injection unit 540 is in fluid communicationwith only the inspiratory gas passage 516. This arrangement provides acompact design of the patient coupling member 510 allowing forunobtrusive placement near a patient. In one aspect, the vapor injectionunit 540 may be oriented along an axis forming an acute angle to thecentral axis of the inspiratory gas conduit 584.

When the vapor injection unit 540 passes through the expiratory gaspassage 514, expiratory air is permitted to flow around the exterior ofthe vapor injection unit 540. Thus, the vapor injection unit 540 injectsvapor directly into the inspiratory gas passage 516 of the patientcoupling member 510 to mix with the inspiratory gas flow. Thisarrangement ensures that only the inspiratory gas passage 516 receivesvapor dispensed from the vapor injection unit 540. Further, the vaporinjection unit 540 may form a tight sealing fit with the access hole 521in the barrier wall 520 of the patient coupling member 510 in order toprevent gas seepage between the expiratory and inspiratory gas passages514, 516. In other aspects, a sealing member such as an O-ring may beprovided between the vapor injection unit 540 and the access hole 521 toprevent gas seepage. In another implementation, the cap or cover 530 maybe located directly adjacent to the inspiratory air passage, and thevapor injection unit 540 may be disposed within the inspiratory gaspassage 516 of the patient coupling member 510 but not within theexpiratory gas passage 514. In some implementations, the vapor injectionunit 540 and the patient coupling member 510 may be separate componentsof a humidification device, such that the vapor injection unit 540 isremovably received within the patient coupling member 510 so that it canbe replaced. In other implementations, the vapor injection unit 540 andthe patient coupling member 510 may be combined to form a singleintegral humidification device.

The vapor injection unit 540 is configured to heat fluid, such as water,and transform it into vapor, such as steam. The vapor injection unit 540is further configured to inject the steam into the inspiratory gaspassage 516 of the patient coupling member 510 in order to providehumidity to a dry inspiratory air flow for a patient to breathe in. Asillustrated in FIG. 16, the vapor injection unit 540 comprises a hollowinjection housing or vapor housing 542 that includes a proximal end 544,an opposite distal end 546, and an inner injection housing lumen 548extending from the proximal end 544 of the injection housing 542 to thedistal end 546 of the injection housing 542. The injection housing 542may have an elongated tubular shape.

In one aspect, the injection housing 542 may be a thermal insulatorcomprising ceramic or other thermally insulating material. For example,the injection housing 542 may comprise material having low thermalconductivity in order to reduce heat transfer through a wall of theinjection housing 542 and into the gas flow. The thermal insulator mayinclude ceramics, glass, composite materials such as glass-bonded mica(Mykroy/Mycalex), fiberglass, insulating plastics, or other suitablematerials having low thermal conductively. The injection housing 542 maybe formed from extruded tubing or another suitable process, such as aninjection molding process.

A cannula 550 may be disposed within the injection housing 542 andincludes an inner cannula lumen 552 configured to receive a fluid. Thecannula 550 may have a fluid supply end 553 configured to receive fluid,such as water, and a vapor dispensing end 554 defining a vapor outletconfigured to dispense vapor. The inner lumen 552 of the cannula 550extends from the fluid supply end 553 to the vapor dispensing end 554.In one implementation, the vapor dispensing end 554 of the cannula 550may have a longitudinal length extending beyond the distal end 546 ofthe injection housing 542 and further defines a vapor outlet 556. Thecannula 550 may be made from materials such as stainless steel, glass,ceramic, or other suitable materials. The cannula 550 may be magnetic ornon-magnetic. In one aspect, the cannula 550 may comprise materialhaving low thermal conductivity.

A hub 560 may be connected to the proximal end 544 of the injectionhousing 542 and is configured to connect to a fluid supply source, suchas a water reservoir. The hub 560 may comprise a fluid inlet 562 forreceiving fluid from the fluid supply source, and a fluid channel 564having a check valve 568 disposed therein. The check valve 568 may be aone-way valve configured to prevent backflow of fluid through the fluidchannel 564. The check valve 568 may be implemented with at least one ofa ball check valve, a diaphragm check valve, a swing check valve, astop-check valve, a pneumatic non-return valve, or another similarmechanical valve. The check valve 568 may close the supply of waterentering the cannula 550 as a result of steam pressure formed within theinner cannula lumen 552.

The hub 560 may be connected to the fluid supply end 553 of the cannula550 such that the fluid channel 564 is in fluid communication with theinner lumen 552 of the cannula 550. The injection housing 542 and thecannula 550 may each have a tubular shape and be concentricallyarranged. In one implementation, the hub 560 may be formed around thefluid supply end 553 of the cannula 550 in an overlapping manner. Thehub 560 may have a standardized Luer connection or a custom connectionconfigured to releasably connect to the fluid supply.

A heater element 570, such as an induction element, may be disposedwithin the inner injection housing lumen 548 of the injection housing542 and span along a length of the injection housing 542 from theproximal end 544 to the distal end 546. In one aspect, the inductionelement 570 may surround at least a portion of the cannula 550. Inanother aspect, the induction element 570 may wrap around and contactthe exterior of the cannula 550. Further, a heating element 572 may beprovided within the inner lumen of the cannula 550, and arranged thereinsuch that a space is provided between the heating element 572 and theinner wall of the cannula lumen 552 to permit a flow of fluid to passtherethrough in order to be heated and transformed into vapor. Theinduction element 570 may be an induction coil formed from a single ormultiple enameled wires. In one implementation in which the inductionelement 570 is formed from multiple wires, the multiple wires may betwisted to form a Litz wire in order to reduce power loss and heatgenerated by the “skin effect” at high alternating current (AC)frequencies. It should further be appreciated that the induction elementmay comprise a rectangular cross-section magnet wire which providessimilar results as the aforementioned Litz wire. Further, according toanother aspect, power to the induction element 570 may be switched toground, or between positive and negative voltages. The voltage waveformmay be square for providing most efficiency, sinusoidal for minimizingEMI, or another waveform such as triangular or sawtooth. The inductionelement 570 may be center-tapped, and a positive voltage may be suppliedat the center tap. The ends of the induction element 570 may bealternately switched to ground to generate an oscillating magnetic fieldwithin the interior of the induction element 570. The oscillatingmagnetic field created from the induction element 570 may produce eddycurrents in order to heat the heating element 572 located within thecannula 550. In other implementations of the disclosure, the heaterelement 570 may be a conduction element, and the heating element 572 maybe a conduction heating element configured to be heated by conduction.

In other aspects, the heater element 570 may be a pair of parallelelectrical conductors configured to generate a dipole. The pair ofparallel electrical conductors may be provided within the injectionhousing inner lumen and extend parallel to its central axis. The pair ofparallel electrical conductors may be insulated wires or conductivetracks formed onto a flexible printed circuit. A positive voltage may besupplied to one of the electrical conductors in order to generate adipole. The two ends of the other electrical conductor may bealternately switched to ground at a high frequency in order to generatean oscillating magnetic field within the injection housing lumen 548.

In further aspects, the heater element 570 may be more than two pairs ofelectrical conductors configured to generate an oscillating magneticfield having multiple poles, such as a quadrupole, hexapole, octupole,or another multipole system with either an even or odd number ofmagnetic poles. The pairs of electrical conductors may similarly extendwithin the injection housing lumen along its central axis. Theelectrical conductors may be insulated wires or conductive tracks formedonto a flexible printed circuit board. A positive voltage may besupplied to one set of electrical conductors. The set of electricalconductors may be alternately switched to ground at a high frequency tocreate a rapidly oscillating magnetic field. In other aspects, a circuitmay be used to switch the polarity of each end of the induction element570 to improve efficiency of the induction element 570.

The induction element 570 may generate an oscillating magnetic fieldwith frequencies up to 200 kHz. In further aspects, electromagneticshielding, specifically radio frequency shielding, may be necessary suchthat the heater assembly 100 meets various regulatory electro-magneticemission requirements.

The vapor injection unit 540 may further include a power and controlsinterface assembly (not shown) connected to the injection housing 542and/or the hub 560. The power and controls interface assembly isconfigured to provide electrical power and control to the inductionelement 570 for heating the heating element 572. In one implementation,the power and controls interface assembly may be integral with the vaporinjection unit 540 to form a single component. In anotherimplementation, the power and controls interface assembly may be aconnector receptacle or other interface adapted to facilitate a quickconnection and/or disconnection with an electrical power source and/orcontrol module. In another implementation, the power and controlsinterface assembly may include an electrical power source and beremovably coupled to the vapor injection unit 540.

The vapor injection unit 540 may also include a thermocouple configuredto measure temperature. The thermocouple may allow a user to monitorand/or provide closed-loop temperature control of the heating element.The thermocouple may be integrated with the heating element as a singlecomponent. In other aspects, the thermocouple may be a separatecomponent from the heating element. For example, the thermocouple may beintegrated into the cannula 550 and/or be placed in contact with thefluid path, which may allow the cannula 550 and/or fluid to act as aconductor, such that at least a portion of the measured thermocouplevoltage is measured across the cannula 550 and/or fluid. In anotherimplementation, the thermocouple may comprise a wire having electricalcontacts (not shown) connected with the power and controls interfaceassembly. The electrical connection may be established using insulatedwires and/or flexible printed circuits. An access opening 566 may beprovided in the hub for passage of wires. It should be appreciated thatthe vapor injection unit 540 may use other devices, such as thermistorsor resistance temperature detectors (RTDs), to measure temperature. Thepower and controls interface assembly may provide electrical power tothe induction element 570 and/or thermocouple electrical contacts.

The thermocouple may be made from a magnetic material, such as Mu-metal,Alumel, iron, nickel, permalloy, or another alloy, to allow thethermocouple to interact with the oscillating magnetic field generatedby the induction element 570 in order to produce heat, thus increasingthe efficiency of the heating element. In some implementations, thethermocouple may be made from the same material as the heating element572 to simplify construction. In other aspects, the thermocouple may bemade from a non-magnetic alloy, or an alloy having low thermalconductivity, in order to reduce generation of induction heating andimprove accuracy of the temperature measurements. Non-magnetic materialsmay include copper, Nicrosil, Nisil, Chromel, Constantan, or othersimilar alloys.

The heating element 572 located within the cannula 550 may be made froma magnetic material such as Mu-metal, Alumel, nickel, iron, permalloy,or other materials with a high relative magnetic permeability. Theheating element 572 may be a tube, a solid cylinder such as a rod orwire, a matrix of cylinders, a sintered cylinder, a porous cylinder, asheet, a spiral sheet, a coil, or any combination thereof. For instance,the heating element 572 may be a twisted or helical coil of wires. Theheating element 572 may extend along the entire length of the cannula550 or along a portion of the cannula. The heating element 572 may beconfigured to interact with the oscillating magnetic field generated bythe induction element 570. The heating element 572 can have a highmagnetic permeability because the efficiency of induction heating withinthe heating element 572 may be greater.

In one implementation, the shape of the heating element 572 core maymatch the shape of the inner cannula lumen 552. In anotherimplementation, the heating element 572 may comprise a rolled foilhaving a jelly roll shape, as illustrated in FIG. 17. The rolled foilheating element 572 comprises a foil 574 that may be spirally wrappedaround a wire or rod mandrel core 576. In another implementation, itshould be appreciated that the heating element may include the spirallyrolled foil 574 but not the mandrel core 576. For instance, the mandrelcore may be optional in order to provide an easier assembly. Further,magnetic fields at the frequencies described herein may induce heat onlywithin about three to four outer layers of the spiral wrapped foil. Inother implementations, the mandrel core 576 may be an axial array ofmagnetic material in the form of wires, rods, plates, or tubes. In someaspects, integration of the mandrel and foil may be in the form ofknurled, drawn or extruded radial flats, grooves, fins or otherfeatures, as well as helical modification thereof. Both the mandrel core576 and the foil 574 may comprise a magnetic material as previouslydescribed, such as Mu-metal, Alumel, nickel, iron, permalloy, or othermaterials with a high relative magnetic permeability.

A gap 578 formed between adjacent layers of wrapped foil 574 provides atortuous pathway for water to travel therethrough. Such a rolled foilheating element 572 permits increased heat transfer to fluid water withminimal restriction to flow through and around the induction heatingelement 572. Thus, the rolled foil heating element 572 can have agreater surface area for contacting fluid to increase the efficiency ofheat transfer between the fluid pumped into the cannula 550 and theheating element 572.

In one aspect of the rolled foil heating element 572 shown in FIG. 17, aMu-metal foil may have a thickness of approximately 0.002 inches orless, and produce higher heat generation for a given induction frequencywhen compared with other selected magnetic materials and thickness. Inanother aspect, the mandrel core 576 may produce a higher heatgeneration for a given induction frequency when compared with otherknown materials (magnetic and non-magnetic). In another aspect, amaximum heat transfer to fluid may occur when a gap of 0.002 inches orless is provided between adjacent layers of the wrapped foil 574 over atotal length of four inches or less. In another aspect, a gap of 0.0005inches (approximately 12 microns) or greater between layers of thewrapped foil 574 over a length of one or more inches may ensure that thefluid remains in contact with the heating element 572 for a duration oftime sufficient to transfer energy (in the form of heat) to water inorder to ensure complete transformation of room temperature water intogas, such as steam. Such evaporation/vaporization of water may bemaximized when the outer diameter of the heating element 572 (i.e., thecombination of the foil 574 and mandrel core 576) is 0.5 inches or less.Moreover, in other aspects, the mandrel core 576 may have a circularcross-section in order to produce optimal heating effects for a givenlength when compared to a mandrel core having a square, pentagonal,hexagonal, or other geometrically shaped cross-section. In otherimplementations, the rolled foil heating element 572 may increaseelectrical inductance by approximately 50% when used in conjunction withrectangular magnet windings having an approximate 4:1 width to thicknessratio, thus indicating increased performance.

Referring to FIGS. 18-20, the vent coupling member 590 is configured tocouple the expiratory and inspiratory gas conduits 582, 584 to aventilator and/or a flow meter to assist with supplying and/orcirculating a flow of gas to the patient, as previously described above.The vent coupling member 590 comprises an expiratory gas inlet 591 andan expiratory fitting portion 592 adapted to sealingly connect to an endof the expiratory gas conduit 582. The vent coupling member 590 furthercomprises at least one inspiratory gas outlet 593 and an inspiratoryfitting portion 594 adapted to sealingly connect to an end of theinspiratory gas conduit 584. The expiratory and inspiratory gas conduits582, 584 may be adapted to mate with the respective expiratory andinspiratory fitting portions 592, 594 of the vent coupling member 590 ina sealing manner, such as with a press-fit connection or a bondedconnection using adhesive, in order to prevent leakage. An annular lip595 may be provided adjacent to the inspiratory fitting portion 594 fora user to grip when connecting or disconnecting the vent coupling member590 from the gas conduits, vent, and/or flow meter.

Expiratory gas that enters the vent coupling member 590 through theexpiratory gas inlet 591 travels through an expiratory gas channel 596and exits through an expiratory gas outlet to the ventilator. Further,dry inspiratory gas supplied from the ventilator enters into the ventcoupling member 590 through an inspiratory gas inlet 598. Theinspiratory gas travels through an inspiratory gas channel 599 and exitsthrough the at least one inspiratory gas outlet 593 into the inspiratorygas conduit 584 of the breathing circuit. In one implementation, theexpiratory and inspiratory gas channels 596, 599 are separated by adividing wall so that expiratory and inspiratory gas does not mix. Inone aspect, the expiratory and inspiratory gas channels may be furtherconcentrically aligned. In another aspect, the inspiratory gas inlet 598and the expiratory gas outlet 597 may be aligned perpendicular to eachother. Similarly, expiratory gas inlet 591 and the expiratory gas outlet597 may be perpendicularly aligned. The dry inspiratory gas may thenflow within the inspiratory gas conduit 584 toward the patient. Theinspiratory gas may enter the at least one inspiratory gas inlet 524 ofthe patient coupling member 510. The dry inspiratory gas may accumulatemoisture transferred from the expiratory gas conduit 582, as will bediscussed in greater detail below. In another aspect, an electricalpower/signal cable 602 and/or fluid supply lumen 604 may be provided inthe breathing circuit. For instance, the power/signal cable 602 and thefluid supply lumen 604 may extend through the vent coupling member 590,one of the breathing gas conduits, and the patient coupling member 510in order to be electrically and fluidly connected, respectively, to thevapor injection unit. In some aspects, the power/signal cable 602 and/orfluid supply lumen 604 may be provided within the expiratory gas conduit582 or the inspiratory gas conduit 584.

A first or pre-heater sensor 536 may be located at the proximal end 517of the patient coupling member 510 at an upstream location of theinspiratory gas flow relative to the vapor injection location. In oneimplementation, the first or pre-heater sensor 536 may be connected toan outer surface of the expiratory fitting portion 532 of the patientcoupling member 510 as shown in FIG. 14. The first or pre-heater sensor536 may be configured to measure a first temperature and a firsthumidity of the inspiratory gas flow prior to the introduction of vaporfrom the vapor injection unit 540. A second or post-heater sensor 538may be located at the distal end 518 of the patient coupling member 510at a downstream location of the inspiratory gas flow relative to thevapor injection location. The second or post-heater sensor 538 may beconnected to an inner surface of the inspiratory gas passage 516 of thepatient coupling member 510 as shown in FIG. 14. The second orpost-heater sensor 538 may be configured to measure a second temperatureand a second humidity of the inspiratory gas flow after vapor has beendispensed into the inspiratory gas flow from the vapor injection unit540. Further, the first and second sensors 536, 538 may each beconfigured to separately measure temperature and humidity independently.In some aspects, the first and second sensors may be spaced equallyapart from the vapor injection location. Further, it should beappreciated that the both the first and second sensors 536, 538 maycomprise a flexible circuit in communication with the power and controlinterface.

A controller in communication with the vapor injection unit 540 via aconnection with the power and control interface may be configured tocontrol an amount of vapor injected into the inspiratory gas passage 516for mixing with the inspiratory gas that enters the patient couplingmember 510. The injected vapor may have a vapor temperature determinedas a function of the measured first and second temperatures and themeasured first and second humidities of the inspiratory breathing gas.

FIG. 21 illustrates a schematic representation of an implementation of aprocess for simultaneously and independently controlling the temperatureand humidity of inspiratory gas in a respiratory breathing circuit usingthe near-patient humidification system described herein. As shown, theprocess comprises supplying a breathing gas to the respiratory breathingcircuit; measuring a first temperature and a first humidity of thebreathing gas at a location upstream from a vapor injection unit;measuring a second temperature and a second humidity of the breathinggas at a location downstream from a vapor injection unit; and injectingvapor from the vapor injection unit into the respiratory breathingcircuit assembly, the vapor having a vapor temperature determined as afunction of the measured first and second temperatures and the measuredfirst and second humidities of the breathing gas. In some aspects, dataprovided by the flow meter may be provided by the ventilator.

Referring again to FIG. 16, for operation of the vapor injection unit540, the induction element 570 may be excited to generate an oscillatingmagnetic field in order to create eddy currents within the heatingelement 572. The eddy currents generated in the heating element 572 mayheat the heating element 572 to a desired temperature. Water may bepumped into the fluid inlet of the hub 560 and past the one-way valve inorder to enter the fluid supply end 553 of the cannula 550. Water passesthe heating element 572 as it travels through the cannula 550 andrapidly absorbs heat, thus vaporizing the water into steam. The rapidexpansion of steam as it forms during vaporization may cause pressurizedsteam to be dispensed from the vapor outlet of the cannula 550 andinjected into the inspiratory gas passage 516 of the patient couplingmember 510 in order to humidify the inspiratory gas flow. It should beappreciated that the process may repeat in a cyclical fashion resultingin steam periodically being injected into the patient's breathingcircuit to humidify the inspiratory breathing gas.

The humidified breathing gas then exits the inspiratory gas outlet ofthe patient coupling member 510 and is directed to a patient interface,such as an endotracheal tube or a breathing mask, for delivery to thepatient. Expiratory gas that is expelled from the patient enters intothe patient coupling member 510 via the expiratory gas inlet 526,travels through the expiratory gas passage 514, and exits from theexpiratory gas outlet 522 directly into the expiratory gas conduit 582.The expiratory gas may travel back toward the vent coupling member 590,where it enters into the expiratory gas inlet 591, passes through theexpiratory gas channel 596, and thereafter exits from the expiratory gasoutlet 597 and into the ventilator.

As further shown in the schematic diagram of FIG. 22, the single-limbimplementation of the humidification system according to the presentdisclosure is configured to provide a moisture transmission pathwaybetween the expiratory gas conduit 582 and the inspiratory gas conduit584, thus lowering the moisture and/or humidity in the flow of breathinggas (BB) expelled from the patient by transferring the moisture and/orhumidity to a dry inspiratory gas flow (DD) provided to the patient. Forexample, the moisture transmission pathway (TT) may occur between thehigher humidity breathing gases in the expiratory gas conduit 582 andthe lower humidity dry gas flow in the inspiratory gas conduit 584. Themoisture level thus may be reduced from within the expiratory breathinggas flow (BB) and transferred to the inspiratory dry gas flow (DD).

In some embodiments, the expiratory conduit 582 may include a permeableportion or membrane along its entire length or a part thereof. Thepermeable portion may be permeable to water vapor but impermeable toliquid water, so that the moisture transmission pathway (TT) is providedby the permeable portion of the expiratory conduit 582. The permeableportion may include one or more materials that are water vaporbreathable and allow for passage of water vapor. The permeable portionmay form some or all of the walls of the expiratory gas conduit 582(e.g., the inner tube) and may include a single, or composite layer ofwater vapor breathable medium. For example, in some embodiments, thepermeable portion may include an inner layer and an outer layer havingdifferent permeability/wicking properties. A first wicking layer may beprovided as an inner layer of inner tube and may be configured tocontact the breathing gas flow (BB) inside of the inner tube. Thewicking layer may be made of one or more wicking materials that allowfor adsorption and/or absorption of moisture and/or water in any phase(e.g., gas and/or liquid), for example, through capillary action. Thepermeable portion may also include an outer layer of water vaporbreathable material that permits the passage of water vapor only, whilepreventing passage of liquid water. It should be appreciated that thepermeable portion may comprise wicking material such as those used withthe moisture removal and condensation and humidity management apparatus410 previously discussed herein.

In some embodiments, the expiratory gas conduit 582 may, additionally oralternatively, include one or more small openings or perforations (notshown) in the inner tube which permit drainage of liquid water from thebreathing gas BB to the dry gas DD. Therefore, a second moisturetransmission pathway may be provided by the one or more perforationsbetween the breathing gas flow (BB) and dry gas flow (BD). It should beappreciated that the transmission pathways may be provided in thealternative and/or at different portions along the breathing circuittubing. Moreover, the transmission pathway (TT) and the secondtransmission pathway may be provided in a gradient along the length ofthe expiratory gas conduit 582. For example, in some embodiments, theinner tube may have more permeability at an upstream end than adownstream end, thus resulting in increased moisture transfer when thebreathing gas enters the breathing gas conduit, and further resulting inreduced condensation in the remaining length of the inner tube. In someembodiments, the inner tube may have more permeability on the downstreamend than the upstream end, thus increasing moisture transfer when themoisture of the breathing gas is lower.

According to another aspect of the present disclosure, a method orprocess for on-demand near-patient humidification provides simultaneous,independent control of the temperature and humidity of the inspiratorygas flow. Control of inspiratory airflow heat and humidity is achievedby the addition of precise control of mass flow and temperature of steaminto a cold, dry airflow. The method or process may comprise a humiditycontrol algorithm. Such an humidity control algorithm considers patientbreathing as either expiration or inspiration. The humidity controlalgorithm also considers each breath in relative time with the startingbreath inhalation t=0. The humidity controls must first determine thepatient breathing rhythm. While the rhythm is indeterminate, thecontrols will heat and inject water as a function of current air flowand temperature. Following detection of the first complete patientbreath, the humidity controls continue to heat and inject water as afunction of current air flow/temp. These water values are collected intoa mathematical array and assigned a relative time in the breath into asecond array. Once the patient's exhalation is complete, the systemwaits for the next inhalation-to-exhalation transition. During the nextpatient breath, the humidity control rotates the calculated water arrayto the end of the array. This data is shifted forward in time by thebreath cycle time period. The formula for the time shifted data may berepresented as: W_(n)(t)=W_(n-1)(t+t_(period)), wherein W_(n) is theprevious patient breath.

For subsequent patient breaths, the system heats and injects the volumeof water corresponding to the time-shifted data calculated from theprevious patient breath, W_(n)(t). The controls continue to calculatewater output as a function of current air flow and stores thisinformation for use in the next patient breath. The controls alsocontinue to wait for the next inhalation-to-exhalation transition, usinginterpolation when actual breath flow measurements do not correspond topredicted values, within a defined tolerance zone. Therefore, if thepatient breathes spontaneously, humidity controls immediately detectthis condition to revert immediately to heating and injecting water as afunction of air flow rate. The humidity controls are effectively resetto initial start-up conditions.

At initial start-up, temperature control temporarily overrides humiditycontrol in priority. A default water flow rate as a function of air flowrate is used during initial start-up. Humidity control begins oncetemperature stability is achieved. The humidity control analyzesabsolute humidity measurements, calculations, or estimates of previouspatient breaths and uses this data to adjust the control algorithm.Because steam possesses significant amounts of energy, a small change inwater flow results in a large change in temperature. Therefore, humidityadjustments must be gradual to maintain temperature stability.Therefore, a running average proves a good control variable for humiditycontrol algorithms. Longer running averages generally provide greaterstability but reduce response time. Shorter running averages sacrificestability for increased response time.

The system for on-demand near-patient humidification of the presentdisclosure permits precise humidity control by controlling the amount ofmoisture in the form of vapor or steam that is mixed within therespiratory airflow. Absolute humidity is determined as the ratio ofmass flow of moisture divided by the volume of dry air. The system mayfurther measure the volumetric (or mass) flow rate of air, and injectsthe appropriate amount of water based on this measurement. The systemmay also permit precise humidity control by controlling the timing whenmoisture is introduced into the air flow, thus preventing humidificationof the airstream during non-inhalation. Whereas conventionalhumidification devices humidify air continuously, which causes PEEP biasflow to be humidified, such excess humidity is wasted and introducesadditional moisture into the exhalation circuit which often generatescondensation. By timing the humidification of the air flow with patientinhalation, the present system is able to reduce water consumption andsubsequent condensation. Moreover, air flow measurements for humiditycontrol may be acquired from data provided by a companion respiratoryventilator or a separate measurement instrument.

Turning to FIG. 23, a flow chart illustrating the aforementioned processfor analyzing the timing of previous patient breaths in order to predictthe next patient breath is shown. This process permits the addition ofheat and moisture in advance of a breath in order to simultaneouslyimprove mixing of humidity into the air flow and improve temperaturecontrol. In a first step S1, the patient breath count is set to zero. Instep S2, the flow meter measurement is read, or data is provided by thevent. If the measured flow does not exceed the bias flow rate thresholdin S3, a value of zero is assigned to the measured data. Real-time datais further collected in a two-dimensional array with a correspondingtimestamp in step S4. In step S5, real-time flow rate data is thenoutput to the control algorithm, and step S2 is then repeated.

Referring again to step S3, if the measured flow does exceed a bias flowrate threshold, then real-time data is collected in a two-dimensionalarray with a corresponding timestamp in step S6. In step S7, adetermination is made as to whether two or more complete breaths havebeen recorded. If two or more complete breaths have not been recorded,then step S2 is repeated. If two or more complete breaths have beenrecorded, then a time shift is determined in step S8 and the flow ratedata is added to the time-shifted two-dimensional array. Thereafter, theflow meter (or vent data) is read in step S9. In step S10, if the actualflow does not correspond to the expected flow, then step S1 is repeated.Alternatively, if the actual flow does correspond to the expected flow,then step S11 is performed which determines whether the measured flowexceeds a bias flow rate threshold. If the measured flow does not exceeda bias flow rate threshold, then a breath is added to the completebreath count, and step S6 is repeated. Alternatively, if the measuredflow does exceed the bias flow rate threshold in step S11, then thereal-time flow rate data is output to the control algorithm in S13.

Measurement of humidity of incoming air can be used to reduce the amountof moisture added to the air flow, thereby improving humidity control.The mathematical formula for rate of water addition to the airstreamassumes incoming air with zero humidity. The flow rate is adjusted tocompensate for incoming humidity within incoming air and/or moistureintroduced through permeable membrane in the expiratory limb of thecircuit. The system is configured to control absolute humidity (mass ofwater vapor divided by the volume of incoming dry air). However, controlof relative humidity (RH) is possible if pressure transducer(s) areincorporated into the system to solve the equations required forcalculating RH. Also, RH control is possible if RH measurementinstruments are incorporated for control feedback. Further, it should beappreciated that additional control may be gained by determining therate moisture is transferred through the permeable membrane, andincluding this rate into the controls algorithm for improved humiditycontrol.

While the system and method for on-demand near-patient humidificationhas been described in terms of what may be considered to be specificaspects, the disclosure need not be limited to the disclosed aspects. Assuch, this disclosure is intended to cover various modifications andsimilar arrangements that fall within the spirit and scope of theclaims, which should be accorded their broadest interpretation so as toencompass all such modifications and similar structures. The presentdisclosure is considered as illustrative and not restrictive.

The invention claimed is:
 1. A near-patient humidification system forproviding vapor to a respiratory breathing circuit, the systemcomprising: an expiratory gas conduit configured to transport anexpiratory gas flow from a patient; an inspiratory gas conduitconfigured to transport an inspiratory gas flow to the patient; apatient coupling member configured to couple the expiratory andinspiratory gas conduits to a patient interface, the patient couplingmember having a housing defining an expiratory gas passage incommunication with the expiratory gas conduit, an inspiratory gaspassage in communication with the inspiratory gas conduit, a proximalend having an expiratory gas outlet and at least one inspiratory gasinlet, and a distal end having an expiratory gas inlet and aninspiratory gas outlet; and a vapor injection unit located at leastpartially within the housing of the patient coupling member, the vaporinjection unit having a vapor housing and a heater assembly, a portionof the vapor injection unit passing through the expiratory gas passageand the expiratory gas being permitted to flow around the portion of thevapor injection unit, the heater assembly configured to heat a supply offluid into vapor and to inject the vapor into the inspiratory gaspassage of the patient coupling member at a vapor injection location forproviding humidity to the inspiratory gas flow, the heater assemblycomprising a heating element and a heater element, the heating elementprovided within the vapor housing and configured to vaporize the supplyof fluid, and the heater element configured to heat the heating element.2. The near-patient humidification system according to claim 1, whereinthe vapor housing includes a proximal end and a distal end, and thevapor housing defining a housing lumen extending from the proximal endto the distal end.
 3. The near-patient humidification system accordingto claim 1, wherein the vapor injection unit further comprises a cannuladefining an inner lumen configured to receive a flow of water, andwherein the inner lumen is in fluid communication with the inspiratorygas passage of the patient coupling member.
 4. The near-patienthumidification system according to claim 3, wherein the heater assemblyis an induction heater assembly, and wherein the vapor injection unitfurther comprises an induction element surrounding at least a portion ofthe cannula.
 5. The near-patient humidification system according toclaim 4, wherein the induction element comprises at least one helicallywound metallic coil.
 6. The near-patient humidification system accordingto claim 4, wherein the induction element comprises one or moreelectrical conductors configured to generate an oscillating magneticdipole.
 7. The near-patient humidification system according to claim 4,wherein the induction element comprises at least two electricalconductors configured to generate an oscillating magnetic multipole. 8.The near-patient humidification system according to claim 7, wherein theat least two electrical conductors are wires or a printed circuit. 9.The near-patient humidification system according to claim 4, the heatingelement being located inside the cannula and at least partiallysurrounded by the induction element; wherein the induction element isconfigured to be excited by electrical current supplied from a powerassembly, to generate an oscillating magnetic field to create eddycurrents in the heating element to heat the heating element, and therebyheat the flow of water in the cannula flowing past the heating element,to thereby vaporize the water into steam which exits the vapor injectionunit to be injected into the inspiratory gas passage.
 10. Thenear-patient humidification system according to claim 9, wherein theheating element comprises Mu-metal.
 11. The near-patient humidificationsystem according to claim 9, wherein the heating element includes amagnetic material with a relative magnetic permeability greater thanone.
 12. The near-patient humidification system according to claim 9,wherein the heating element comprises a rolled foil spirally disposing aplurality of layers of said foil.
 13. The near-patient humidificationsystem according to claim 9, wherein the heating element comprises awire mandrel and a foil wrapped around the wire mandrel in a spiralpattern disposing a plurality of layers of said foil.
 14. Thenear-patient humidification system according to claim 1, wherein thepatient coupling member housing includes the proximal end configured toreleasably engage the expiratory and inspiratory gas conduits, and thedistal end configured to releasably engage a patient interface.
 15. Thenear-patient humidification system according to claim 1, furthercomprising a vent coupling member adapted to releasably couple theexpiratory and inspiratory gas conduits to a ventilator.
 16. Thenear-patient humidification system according to claim 1, wherein theexpiratory and inspiratory gas conduits are concentrically arranged,such that the expiratory gas conduit defines an inner conduit and theinspiratory gas conduit defines an outer conduit.
 17. The near-patienthumidification system according to claim 16, wherein the expiratory gasconduit is configured to permit moisture to permeate through walls ofthe expiratory gas conduit so that humidity or water vapor in theexpiratory gas flow can be transferred to the inspiratory gas flow inthe inspiratory gas conduit.
 18. The near-patient humidification systemaccording to claim 1, further comprising a first sensor configured tomeasure a temperature and a humidity of the inspiratory gas flowindependently at a location upstream from the vapor injection location,and a second sensor configured to measure a temperature and a humidityof the of the inspiratory gas flow independently at a locationdownstream from the vapor injection location.
 19. The near-patienthumidification system according to claim 1, wherein the vapor housinghaving a proximal end and a distal end, the vapor housing defining ahousing lumen extending from the proximal end to the distal end, andwherein the vapor injection unit includes a hub connected to theproximal end of the vapor housing and being configured to connect to afluid supply.
 20. The near-patient humidification system according toclaim 1, further comprising a check valve proximal to the heatingelement.
 21. The near-patient humidification system according to claim1, wherein the vapor housing having a proximal end and a distal end, thevapor housing defining a housing lumen extending from the proximal endto the distal end, and wherein the vapor housing comprises a thermallyinsulating material.
 22. The near-patient humidification systemaccording to claim 1, wherein the vapor housing having a proximal endand a distal end, the vapor housing defining a housing lumen extendingfrom the proximal end to the distal end; wherein the vapor injectionunit further comprises a cannula defining an inner lumen configured toreceive a flow of water; wherein the inner lumen is in fluidcommunication with the inspiratory gas passage of the patient couplingmember; and wherein the cannula is made from a material selected frommetal, plastic, glass, ceramic, and a combination thereof.
 23. Thenear-patient humidification system according to claim 1, wherein thevapor injection unit further comprises a power assembly for connectionto an electrical power source.
 24. The near-patient humidificationsystem according to claim 23, wherein the power assembly is located at aproximal end of the vapor housing.
 25. A method of simultaneously andindependently controlling the temperature and humidity of inspiratorygas in a respiratory breathing circuit, the method comprising: providingthe near-patient humidification system as claimed in claim 1; supplyinga breathing gas to the respiratory breathing circuit; measuring a firsttemperature and a first humidity of the breathing gas at a locationupstream from the vapor injection unit; measuring a second temperatureand a second humidity of the breathing gas at a location downstream fromthe vapor injection unit; and injecting vapor from the vapor injectionunit into the respiratory breathing circuit, the vapor having a vaportemperature determined as a function of the measured first and secondtemperatures and the measured first and second humidities of thebreathing gas.